I. Field of the Invention
The present invention relates generally to antennas for wireless devices. More specifically, the present invention relates to a stacked dielectric resonator antenna assembly that uses a conductive skirt in contact with the ground plane to adjust the directivity of the antenna radiation patterns. Furthermore, the present invention relates to a low profile dielectric resonator antenna assembly for use with satellite or wireless communication systems.
II. Description of the Related Art
Recent advances in wireless communication devices, such as mobile and fixed phones for use in satellite or cellular communications systems, have motivated efforts to design antennas more suitable for use with such devices. New antennas are generally needed to meet design constraints being imposed on new devices including overall size, profile, weight, and manufacturability. Several factors are usually considered in selecting an antenna design for a wireless device or phone, such as the size, the bandwidth, and the radiation pattern of the antenna.
The radiation pattern of an antenna is a very significant factor to be considered in selecting an antenna. In a typical application, a user of a wireless device such as a mobile phone needs to be able to communicate with a satellite or a ground station that can be located in a variety of directions relative to the user. Consequently, an antenna connected to the wireless device should preferably be able to transfer, transmit and/or receive, signals from may directions. That is, the antenna should preferably exhibit an omni-directional radiation pattern in azimuth and a wide beamwidth (preferably hemispherical) in elevation.
Another factor that must be considered in selecting an antenna for a wireless device is the antenna bandwidth. That is, the useful range of frequencies over which the antenna efficiently transfers signals without an undesirable amount of loss. As an example, a typical wireless phone transmits and receives signals at separate frequencies. For example, a Personal Communication Services or PCS type phone operates over a frequency band of 1.85-1.99 GHz, requiring a bandwidth of 7.29%. A typical cellular phone operates over a frequency band of 824-894 MHz which requires an 8.14% bandwidth. Some satellite communication systems may have even wider bandwidth requirements. Accordingly, antennas for wireless phones used in such systems must be designed to meet these larger bandwidths.
Currently, monopole antennas, patch antennas, and helical antennas are among the various types of antennas being used in satellite user terminals or phones and other wireless-type devices. These antennas, however, have several disadvantages, such as limited bandwidth and large size. These antennas also exhibit a significant reduction in gain at lower elevation angles (for example, around 10 degrees), which makes them undesirable for use in satellite phones where a given satellite used for communication may frequently be near this low elevation.
An antenna that appears attractive for use in wireless user terminals or phones is the dielectric resonator antenna. Generally, dielectric resonators are fabricated from low loss materials that have high permittivity. Until recently, dielectric resonator elements have only found use in microwave circuits, such as in filters and oscillators. However, dielectric resonator antennas have been proposed and designed for wireless applications as described in U.S. patent application Ser. No. 09/150,157 entitled xe2x80x9cCircularly Polarized Dielectric Resonator Antennaxe2x80x9d filed Sep. 9, 1998, now U.S. Pat. No. 6,147,647 assigned to the same assignee, and incorporated herein by reference.
Dielectric resonator antennas offer several advantages over other antennas, such as small size, high radiation efficiency, and simplified coupling schemes for various transmission lines. The bandwidth can be controlled over a wide range by the choice of dielectric constant (∈r), and the geometric parameters of the resonator. Such antennas can also be made in low profile configurations, making them more aesthetically pleasing than standard whip, helical, or other upright antennas. A low profile antenna is also less subject to damage than other upright style antennas. Therefore, dielectric resonator antennas appear to have significant potential for use, for example, in mobile or fixed wireless phones for satellite or cellular communications systems.
However, one problem encountered in using current dielectric resonator antenna designs is the requirement for multiple signal leads to achieve desired circularly polarized radiation patterns. That is, not unlike some patch antennas, two signal feeds are required which are separated in position by what is termed 90 degrees of phase. The ability to handle circularly polarized radiation is critical to applications such as Low Earth Orbit (LEO) satellite communication systems. Generally, the two signal feeds are positioned on the perimeter of the dielectric material. The requirement for two very low loss cables, that need to be substantially identical or matched in impedance to prevent an unbalanced feed structure places undesired restrictions on antenna placement and design.
Not only is circularly polarized radiation employed in some communication systems, but two antennas are often used, one for transmitting and one for receiving. In addition, there are plans to use multiple receiving and transmitting antennas to mitigate the affects of specular reflection, or arrays to create specially tailored radiation patterns that provide improved gain for horizon-to-horizon coverage or multiple satellite communications. In any case, it is very inconvenient and sometimes impractical to manufacture antenna assemblies with multiple antennas having two or more signal leads per antenna element, along with associated cables, connectors, and matching circuits. Each item or component, including cables, added to multiple antenna structures consumes room, making the structure undesirably larger, and makes it more difficult to physically assemble. It is also evident that the more components involved in any assembly make it more costly to manufacture, and may decrease operational reproducibility and reliability.
What is needed is an antenna structure that can maintain a desired polarization configuration, provide efficiently tailored radiation patterns, while allowing simplified signal transfer, impedance matching, and manufacturing or assembly.
The present invention is directed to a dielectric resonator antenna having a ground plane formed of a conductive material, and a resonator formed from a dielectric material mounted on the ground plane. The ground plane extends beyond the edge or periphery of the resonator is shaped so that it extends downward from a lower portion of the resonator material, forming a conductive skirt about a main or central portion of the ground plane. A ground plane is typically formed as a conductive layer of material on top of a support substrate such as a multi-layered printed circuit board material.
At least one, and generally two signal probes are electrically coupled to the resonator to provide first and second signals, respectively, to the resonator, and produce circularly polarized radiation in the antenna. Preferably, the resonator is substantially cylindrical, although rectangular, elliptical shapes or other shapes may be used as desired. The dielectric material may have a central axial opening therethrough. Also preferably, the first and second probes are spaced approximately 90 degrees apart around the perimeter of the resonator.
In a further embodiment, the invention is directed to a dual band dielectric resonator antenna, having a first dielectric resonator mounted on a first ground plane formed of a conductive material, and a second resonator mounted on a second ground plane formed of a conductive material. The first and second ground planes are separated from each other by a predetermined distance, and each has an outer portion that extends downward. First and second probes are electrically coupled to each of the resonators and are spaced approximately 90 degrees apart around the perimeter of each resonator to provide first and second signals, respectively, to each resonator. Each of the resonators resonates in a predetermined frequency band that differs between the resonators. Support members mount the first and second ground planes in spaced apart relation with a predetermined separation distance such that the central axes of the resonators are substantially aligned with each other.
In a still further embodiment, the invention is directed to a multi-band antenna assembly in which first and second dielectric resonators are each mounted on a central portion of a ground plane formed of conductive material. The first and second ground plane central portions are mounted inside a radome separated from each other by a predetermined distance. An outer edge of each ground plane main portion makes contact with a conductive skirt formed on an interior wall of said radome adjacent to where each is mounted. Each ground plane central portion is electrically connected to a corresponding conductive skirt.
In further embodiments, the skirts are each deposited on the radome inner wall by plating. The radome has two rims formed on said inner surface, one located where each ground plane central portion is to be mounted, and for supporting said ground plane. Each ground plane is connected to a corresponding skirt by physical contact therewith, or by using electrically conductive material disposed on or contacting said ground plane and skirt.